Complex of 2,6-dimethylnaphthalene and 2-cyano-6-methylnaphthalene

ABSTRACT

A complex of 2,6-dimethylnaphthalene (2,6-DMN) and 2-cyano-6methylnaphthalene (2,6-CMN) is formed by treating 2,6-DMN with 2,6-CMN. The complex is useful as a source of 2,6-DMN which is purer than the 2,6-DMN from which the complex can be made.

United States Patent 1 [1 1 ,870,745

Angstadt Mar. 11, 1975 [54] COMPLEX 0F 3,670,039 6/1972 Davis 260/6742,6-DIMETHYLNAPHTHALENE AND 2-CYANO-6-METHYLNA HT PrimaryExaminer-Elbert L. Roberts [75] Inventor: Howard P. Angstadt, Media, Pa.Asslsmm Exammer l')olph Terrence Attorney, Agent, or Fzrm-George L.Church; Donald [73] Ass1gnee: Sun Ventures, Inc., St. Davlds, Pa. RJohnson; Edward Hess [22] Filed: Oct. 29, 1973 [21] Appl. No.: 410,650[57] ABSTRACT A complex of 2,6-dimethylnaphthalene (2,6-DMN) [52] US.Cl. 260/465 R, 260/674 N a d 2-yan0-fi-methylnaphthalene (2,6-CMN) i5[51] Int. Cl. C07c 121/62 f d by treating 2 with 2 The of Search R, Nomplex is usefu] as a Source of is purer than the 2,6'DMN from which thecomplex can [56] References Cited be made UNITED STATES PATENTS3,665,044 5/1972 Scott 260/674 D'awmgs 1 COMPLEX OF2,6-DIMETHYLNAPHTHALENE AND 2-CYANO-6-METHYLNAPHTHALENE CROSS REFERENCETO RELATED APPLICATION Copending application, Ser. No. 410,649, filed ofeven date herewith by Howard P. Angstadt, discloses and claims a processfor separating 2,6-DMN from a DMN isomer mixture by means of the 2,6CMN-2,6- DMN complex claimed herein.

BACKGROUND OF THE INVENTION 2,6-DMN is useful in the manufacture ofsynthetic polyester fibers. It is well known that for this purpose the2,6-DMN must be very pure as other DMN isomers seriously detract fromthe quality of the resulting fiber. The 2,6-DMN can be obtained fromcertain petroleum fractions where it occurs naturally or it can be madesynthetically such as by the procedure described in copendingapplication of Sheldon L. Thompson, Ser. No. 263,731, filed June 9,1972. Use of either source of 2,6-DMN involves the problem of separatingthe 2,6- DMN from other DMN isomers, i.e., from mixture ofalkylnaphthalenes. For example, although petroleum fractions such asheavy reformate bottoms and catalytic gas oils contain 2,6-DMN, all theother DMN isomers are also present. It is essentially impossible toseparate 2,6-DMN from the fraction by distillation because of thecloseness of the boiling point of 2,6-DMN to other isomers. For example,2,6- and 2,7-DMN both boil at 504F.

When made synthetically the same problem often arises. The aforesaidThompson application discloses a process wherein o-xylene is reactedwith butadiene to form o-tolylpentene-Z which is then dehydrocyclized tol,5-dimethyltetralin and the latter is dehydrogenated and thenisomerized to 2,6-DMN. Unfortunately the 2,6-DMN is found to alsocontain some 2,7-DMN for two reasons. One, any p-xylene contaminant inthe oxylene feed follows the corresponding reactions as the o-xyleneresulting in 2,7-DMN. Secondly, in the isomerization step small amountsof 2,7-DMN are formed.

Accordingly a source of DMN of high purity is highly desirable.

SUMMARY OF THE INVENTION A source of high-purity 2,6-DMN is the complexformed between 2,6-DMN and 2,6-CMN. When the complex is heated to theboiling point of 2,6-DMN the latter is distilled off as a pure productleaving solid 2,6- CMN behind. Since the complex can be formed from the2,6-DMN in an impure mixture thereof, i.e., from a relative impure2,6-DMN, the complex is a desirable source of relatively pure 2 ,6-DMN.

DESCRIPTION OF THE INVENTION The 2,6-DMN component of the complex can ofcourse be pure 2,6-DMN but is preferably a mixture of DMN isomerscontaining 2,6-DMN. Such mixtures are found in petroleum fractions suchas a heavy reformate bottoms or a catalytic gas oil having a boilingrange of say 460-650F. Such fractions will usually contain -30 percent2,6-DMN and l-% each of most of the other DMN isomers. If the catalyticgas oil fraction is fractionated to separate a 460540F fraction the DMNsare retained but certain other unwanted material such astrimethylnaphthalenes are removed.

Alternatively the DMN isomer mixture can be a stream containingsubstantially all 2,6-DMN with very minor amounts, e.g. less than 5percent, of, say, one other isomer such as the 2,7-isomer. Such a streamcan be obtained in the aforesaid Thompson process.

The 2,6-CMN is obtained by heating 2,6methylnaphthalenecarboxylic acidat l50-30()C in the presence of ammonia and an alumina or zeolitedehydrating agent. The 2,6-methylnaphthaleneca'rboxylic acid can beobtained according to the procedure described in U.S. Pat. No.3,340,155, issued Sept. 5, l967 to .l. D. Douros, Jr. et al.

The complexing can be carried out by contacting the 2,6-CMN with theliquid DMN isomer mixture. The petroleum fractions containing 2,6-DMNare of course liquid at ambient conditions. If a solid mixture of, say,2,6- and 2,7-DMN is employed, as might be obtained from a synthetic2,6-DMN process, the mixture should be dissolved in a solvent such aspetroleum ether. The 2,6-CMN is also soluble in petroleum ether but thecomplex is less soluble and therefore precipitates. The exact solubilityof the complex in ether is not known but etherzcomplex weight ratios ofabout 10:1 are generally satisfactory.

The complex contains equal molar amounts of 2,6- CMN and 2,6-DMN. Theamount of 2,6-CMN employed is preferably less than or equal to one moleper mole of 2,6-DMN in the DMN isomer mixture.

The 2,6-CMN is not very soluble at room temperature in a petroleumfraction DMN isomer mixture and such a mixture plus 2,6-CMN ispreferably heated to above 30C, say 60-65C, to speed dissolution of theCMN which, once in solution, complexes with the 2,6- DMN isomer almostimmediately. After the complex is formed the entire mass is cooled toeffect precipitation of the complex. Cooling to or somewhat above roomtemperature is usually adequate and cooling too far below this isdisadvantageous since material other than the 2,6-DMN:2,6-CMN complexwill ultimately also precipitate. If petroleum ether or the like is thesolvent for the DMNs heating and cooling is not necessary since the DMNsand 2,6-CMN are soluble in ether at room temperature whereas the complexis less soluble and therefore precipitates.

As noted above the complex is useful as a source of relatively pure2,6-DMN. For example, heating the complex to the boiling point of2,6-DMN (262C at 1 atm) causes the complex to decompose liberating 2,6-DMN (melting point 108C) and leaving liquid 2,6- CMN (melting pointl28-l29C).

The recovered 2,6-DMN will usually be essentially pure, i.e., a purityabove percent by weight. The exact purity will vary depending upon theefficiency of the filtration or other separation steps employed, but thefinal 2,6-DMN product can if desired be recrystallized from alcohol toeffect a final purification. Purities lower than 95 percent will beobtained if, for example, the cooling step is carried out at too low atemperature so that an impure complex is separated.

EXAMPLE I Equal molar amounts of 2,6-DMN and 2,6-CMN are added topetroleum ether at room temperature. A precipitate quickly forms andafter several minutes stirring it is filtered off. lts carbon, hydrogenand nitrogen analysis is in good agreement with the calculated values,

viz,

Upon heating the precipitate to 130C no component melts which shows thatit is not a simple mixture. 2,6- DMN melts at 108C and 2,6-CMN at 129Cand it is well known that a simple mixture of the two would result in acomposition having a melting point lower than either constituent.

A vapor phase chromatographic analysis of the complex shows two peaks ofequal area and having retention times equal to those of pure 2,6-DMN and2,6- CMN. This shows the molar ratios of components and that under theconditions of the determination the complex is split into its componentparts. No other peaks were present.

EXAMPLE 11 One gram of a 460-650F catalytic gas oil was mixed with2,6-CMN in the ratio of one mole of the latter per mole of 2,6-DMN inthe gas oil. The mixture was heated to 60-75C and the 2,6-CMN dissolved.The solution was then cooled to room temperature and the resultingprecipitate separated by filtration. The precipitate was analyzed byVPC, which effected a separation of the two components thereof, andshown to have an equal molar 2,6-DMN and 2,6-CMN composition.

The purity of the 2,6-DMN was 99-100 weight percent. The analysis (inweight percent) of the original gas oil is as follows:

Low ends Naphthalene 2-Ethylnaphthalene Biphenyl 2,6-DMN 2,7-DMN 1,7-DMNHeavy ends mixture of dimethylnaphthalene isomers.

1. As a composition a substantially equimolar complex of2,6-dimethylnaphthalene and 2-cyano-6-methylnaphthalene.
 1. AS ACOMPOSITION A SUBSTANTIALLY EQUIMOLAR COMPLEX OF 2,6-DIMETHYLNAPHTHALENEAND 2-CYANO-6-METHYLNAPHTHALENE.
 2. Composition according to claim 1wherein the 2,6-dimethylnaphthalene component is derived from a mixtureof alkylnaphthalenes.